1. Field of the Invention
This invention relates to an apparatus for transferring electronic parts or the like from hoppers to specific locations, and more particularly is directed to an apparatus for transferring chip-type circuit elements from hoppers to specific locations in a template by which the elements are pre-positioned for mounting on a printed circuit board or a hybrid integrated circuit.
2. Description of the Prior Art
Printed circuit boards are commonly used for the assembly of electronic circuits. A printed circuit board consists of an insulating substrate with a pattern of conductors printed on one or both sides thereof for interconnection of parts and for connection to external circuits. Conventional assembly methods include inserting wire leads of electronic components through holes or connecting them to posts for temporarily affixing them to the circuit board until a single conventional soldering operation mechanically and electrically connects the leads of the circuit board. The art of computer-controlled manual insertion of such conventional parts onto circuit boards with little or no hand labor is now well advanced.
Chip-type circuit elements are now employed to perform the functions of a number of active and/or passive elements in an electronic circuit, thereby to increase the circuit density and improve the reliability of the resulting circuit. Chip-type elements are usually formed as cylinders having end caps at the ends with terminals for direct soldering to conductors on the circuit board rather than the wire leads provided on the earlier conventional components. Such chip-type elements, being very small and lacking wire leads, resist automatic insertion in the circuit board by conventional automatic insertion machinery prior to attachment by the soldering operation.
Installing chip-type elements by manual placement of the chip-type circuit elements one-by-one at predetermined positions on the circuit board obviously involves unacceptably tedious and costly labor. Usually, the chip-type elements are temporarily secured to the circuit board using an adhesive resin until the soldering operation is completed.
In order to avoid the above objections to the manual placement of chip-type circuit elements, it has been proposed to feed the elements from hoppers through transferring tubes which convey them by gravity and/or by air under pressure to specific locations in a template which positions a set of the chip-type circuit elements in the relative translational and rotational orientations required for mounting a printed circuit board. The chip-type circuit elements can thereupon be temporarily affixed, as a set, at appropriate locations on a printed circuit board which has been previously prepared with a corresponding pattern of adhesive resin.
Transfer of the chip-type circuit elements from the hopper to the template has conventionally been performed with transferring tubes of circular cross-section. It has been found that the generally cylindrical chip-type circuit elements undergo rotational and vibrational motions while being transferred through such cylindrical transferring tubes. Such vibration and rotation decreases the speed of transfer of the elements by factors of 10 or 20 compared to the transferring speed which can be attained if the elements are prevented from vibrating and/or rotating. Thus, the transfer operation takes 10-20 times longer than would otherwise be required, and the reliability of the operation is degraded.
One measure that has been employed to prevent vibration of the chip-type circuit elements in travelling through the transferring tube is a tensioned wire passing down through the interior of the transferring tube to interfere with stable vibration and rotation of the chip-type circuit elements as they pass therethrough. Although usually effective to speed up the transfer of the circuit elements through the transferring tube, the provision of a wire in the transferring tube is expensive and it is difficult to control the tension thereof for proper damping of vibration of the chip-type circuit elements as they pass through the tube. Furthermore, the wire increases the tendency of the elements to choke the tube and block the transfer of elements therethrough.